can someone please help me with this? easy question?

Question

Consider a steel guitar string of initial length L=1m and cross-sectional area A=0.5mm^2. The Young's modulus of the steel is Y= 2.0 x10^11 pa. How far (delta L) would such a string stretch under a tension of 1500 ?
Express your answer in millimeters using two significant figures.

i need a step by step guide. the answer is 15mm but i keep getting 66.67mm. 
what i did was, 
1500/0.5mm^2 = 3000Nmm^-2.
then i convert 2 x10^11 Pa to Nmm^-2 = 200 000Nmm^-2
then, 3000Nmm^2 / 200 000Nmm^-2 = 0.015

using formula, (F/A) / (L/delta L) =Y, 
1/0.015 = 66.67mm^2

that's what i got. i know it's wrong, so tell me where did i go wrong please..

Algol · Accepted Answer

Looks like you are using mixed units, that is, you aren’t converting the given cross-sectional area to square meters (the only data you have which is not already in SI units).  Start with this equation:

F/A = YΔL/L₀

Solve for change in length:

ΔL = FL₀/AY--------------->A = 0.50mm² = 5.0 x 10^-7m²
= 1500N(1.0m) / (5.0 x 10^-7m²)(2.0 x 10¹¹Pa)
= 0.015m (or 15mm)

Hope this helps.

Anonymous · Answer

ANything by Michelle Branch or the Dixie Chicks. Wonderwall is pretty easy. Wish You Were Here by Pink Floyd. You might need a capo for some of that stuff.

can someone please help me with this? easy question?

2 Answers